The present invention relates generally to intravascular catheters. More particularly, the present invention relates to intravascular catheters adapted to make measurements within the body of a patient.
Therapy modalities for heart disease have traditionally focused on treating blood vessels which have become occluded (blocked) or stenotic (narrowed) by calcified plaque deposits. Blood vessels that have become occluded or stenotic in this manner may interrupt the flow of blood that supplies oxygen to the heart muscle. Occluded or stenotic blood vessels may be treated with a number of medical procedures including angioplasty and atherectomy. Angioplasty techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) are relatively non-invasive methods of treating restrictions in blood vessels. In these procedures, a balloon catheter is advanced over a guidewire until the balloon is positioned proximate a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened. During an atherectomy procedure, the stenotic lesion is mechanically cut or abraded away from the blood vessel wall using an atherectomy catheter.
Calcified plaque deposits typically comprise hard materials. Plaque may also comprise soft materials or combinations of soft and hard materials. Soft plaque typically comprises deposits of cholesterol and other fats which build up within the blood vessels as a patient ages. The build up of plaque in the blood vessels is sometimes referred to as atherosclerosis, or hardening of the arteries.
Atherosclerosis often begins as a small injury to an artery wall. This injury triggers a cyclic cascade of injury and response, inflammation, and healing, which may ultimately lead to the narrowing of the artery. As the atherosclerotic plaque worsens, inflammatory cells, especially macrophages, collect at the site to isolate the debris of the damaged tissue. The result is a core of lipid, macrophages or foam cells and nectrotic tissue, covered by a fibrous cap of scar tissue. If the fibrous cap becomes weakened or is subjected to excessive stress, it may rupture, exposing the thrombogenic contents of the core to the blood stream. If the resulting blood clot is severe enough, it may occlude the artery. If this obstruction persists in a coronary artery, a myocardial infarction may result.
Plaque deposits with a risk of rupturing are sometimes referred to as vulnerable plaque. Vulnerable plaque typically comprises a core of soft materials covered with a fibrous cap. Many vulnerable plaque deposits do not limit the flow of blood through the blood vessels. It has recently been appreciated that vulnerable plaques that do not limit flow may be particularly dangerous because they produce no warning symptoms, but can rupture suddenly causing heart attack and death. This may occur, for example, when the vulnerable plaque ruptures, forming a blood clot inside the blood vessel lumen and causing a blockage.
Recently, the pivotal role of inflammation in the progression of atherosclerosis has been recognized. A systemic increase in temperature is often associated with infection (e.g., a fever). Likewise, a local infection or localized damage to tissue may result in a localized increase in temperature. An increase in temperature is thought to be caused by the response of the immune system to infection, known as inflammation. It has been observed that the inflamed necrotic core of a vulnerable plaque maintains itself at a temperature that may be one or more degrees Celsius higher than that of the surrounding tissue. For example, an inflamed plaque in a human heart, where the normal temperature is about 37xc2x0 C. may be at a temperature as high as 40xc2x0 C.
The present invention is directed to methods and devices for the detection of vulnerable plaque within an artery. A device in accordance with one embodiment of the present invention includes an elongate shaft having a distal end and a proximal end. A detector assembly is fixed to the elongate shaft proximate the distal end thereof.
In one method in accordance with the present invention, a catheter including a detector assembly disposed within a balloon is provided. The catheter is advanced through the vasculature of a patient until a distal end of the catheter is proximate a target region of a vessel. The balloon of the catheter is then inflated, for example, with a gas. When the balloon is inflated, blood within the vessel is displaced. The detector assembly detects infrared radiation from the body of the patient. In a preferred method, the infrared radiation is absorbed by the detector assembly and converted to an electrical signal. The electrical signal is transmitted to an external display and/or recording device. In an additional method in accordance with the present invention, a bolometer is placed proximate a target tissue.